The present invention relates to an abrasion and impact resistant composite castings for working in condition of wear and high dynamic loads.
Such composite castings must have high degree of wear resistance in combination with high ductility and impact strength. They can be used to the service life of mining and heavy construction equipment, such as bucket wheel excavators, dragline, excavators, high capacity dump trucks and crushing/milling machines.
The above mentioned equipment and its parts such as buckets of excavators, draglines, loaders, discharge throats, chutes after jaws and cone (gyratory) crushers and the like are subjected to intense abrasive wear with impact loads that cause high stresses of the surface of the parts.
Some composite castings and methods of their manufacture are disclosed in U.S. Pat. No. 5,328,776 and SU 4,061,345 and RU 308,625. In the book Garber, M. E., “Casting made of White Wear Resistant Cast Irons”, Mashinostroenie, Moscow, 1972, it was shown that diminution of dimensions of carbides in casting of white irons due to acceleration of crystallization increases their wear and impact resistance. Therefore it is advisable to use different methods of comminution of carbides in wear resistance alloys, that are used for inserts of composite castings. However, when intensity impact loads reach large amounts, the service life of the composite castings with white chromium cast iron inserts do not exceed the service life of low carbon martensite steel. In the publication Katovich “Wear” 1978, V. 48, S. 35-53 it is shown that during wear the quartz sand at speed of abrasive treatment 70 m/sec and angle of attack 90° white chromium cast iron 15-3, hardness 554 Hv had a wear resistance equal to 0.6 of reference composed of carbon steel.
Low wear resistance of inserts of white chromium cast irons during wear with high stresses is caused by brittleness of carbides Cr7C3 which have a hexagonal crystal lattice with a significant difference between parameters of the lattice a and c, which reaches three times.
It is also necessary to mention that acceleration of crystallization of cast irons to a certain limit diminishes the dimensions of carbides, but does not liquidate their dendritic structure, which reduces resistance to wear and impact loads.